1. Field of the Invention
The present invention relates generally to an image forming device and, more particularly, to a reinforced doctor blade assembly seal and a printer cartridge employing the reinforced seal.
2. Description of the Related Art
An image forming device, such as a laser printer and the like, includes a drum having a photoconductive outer cylindrical surface charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. Those areas of the photoconductive surface exposed to light are discharged thus forming a latent electrostatic image thereon. A developer material, such as toner, having an electrical charge such that the toner is attracted to the discharged area of the photoconductive surface operates in contact with the photoconductive surface. The drum developed image then rotates toward a transfer station. A recording sheet is then brought into contact with the photoconductor and the toner thereon is transferred to the recording sheet in the form of the latent electrostatic image. The recording sheet is then heated, permanently fusing the toner to the sheet. In preparation for the next image forming cycle, the photoconductive surface of the drum is cleaned of residual toner and recharged. U.S. Pat. No. 6,990,308, assigned to the assignee of the present invention, discloses an image forming device having the aforementioned configuration. The disclosure of this patent is hereby incorporated herein by reference thereto.
Typically, as seen in the cited patent, the toner is stored in a toner well or reservoir of a printer cartridge located adjacent to the drum. A doctor blade assembly and a developer roll of a developer unit, which is part of the printer cartridge, are positioned between the toner reservoir and the drum for controlling the amount of toner delivered to the drum. A nip created between the doctor blade of the doctor blade assembly and the developer roll controls the thickness of the toner layer formed on the developer roll. To be able to print correctly, toner must be evenly distributed, or doctored, out in a thin uniform layer onto the developer roll in the proper thickness. This function is performed by the doctor blade.
Referring to FIGS. 1, 2A and 2B herein, there is partially shown in FIGS. 2A and 2B the printer cartridge 10 in which a seal 12 in the form of an elongated strip of a flexible plastic film is positioned between the doctor blade assembly 14 and a portion of a housing 16 of the printer cartridge 10. The housing portion is in the form of a corner 16a on the housing 16. The strip of film comprising the seal 12, shown by itself in FIG. 1, is a bi -axially-oriented PET (boPET) polyester film material, marketed under the trademark Mylar. It is positioned in a space or gap 18 between the doctor blade assembly 14 and the corner 16a on the cartridge housing 16 in order to prevent leaking of toner from between these components through this gap 18. Referring to FIG. 1 herein, this seal, generally designated 12, is shown by itself. In FIG. 2A the seal 12 is shown correctly installed and positioned in the printer cartridge 10, closing the gap 18 between a bracket 20 of the doctor blade assembly 14 and the housing 16 of the printer cartridge 10.
The developer roll 22, a toner adder roll 24 and the doctor blade assembly 14, with the doctor blade 26 mounted by the bracket 20, make up the developer unit 28 and are mounted on the housing 16 of the printer cartridge 10, as shown in FIGS. 2A and 2B. The quantity of toner in the toner reservoir of the printer cartridge 10 is depleted through use in the printing operation. Thus the printer cartridge 10 is a consumable item which must be replaced periodically in the image forming device. Being a consumable, the printer cartridge 10 must be designed and manufactured to withstand rough handling during shipping, separate from the printer, through the supply chain to a customer and installation into an image forming device. The printer cartridge 10 has the potential to be dropped and thus exposed to large shock forces during shipping separate from the printer.
Dropping the printer cartridge 10 can lead to excessive toner leaks from behind the doctor blade assembly bracket 20 due to internal pressure forcing the doctor blade assembly seal 12 to blow out and dislocate from its correct sealing position, as seen in FIG. 2A, to the blown-out position, as seen in FIG. 2B. A photograph of the blown-out position of the seal 12 replicated by a drop test is shown in FIG. 2C. This blow out and dislocation of the seal 12 causes two problems. First, when the seal 12 is pushed out over the doctor blade assembly 14 as shown in FIG. 2C, its sealing integrity is lost and toner can easily leak from the printer cartridge 10. Second, as shown in FIG. 2B the seal 10 may assume a wedged condition upstream of the gap 18 and on top of the doctor blade assembly 14 where it applies increased downward force onto the doctor blade 26, adversely affecting the doctoring performance of the doctor blade 26.
One proposed solution for avoidance of the blow out problem has been to use a seal in the form of a strip of foam material, rather than of the boPET polyester material, behind the doctor blade assembly. However, the presence of the foam tends to prevent the doctor blade 26 from translating smoothly against the developer roll 22. Also, the foam causes more leak paths to propagate than the boPET polyester seal, requiring the application of wax to fill the anticipated leak paths.
Thus, there is a continuing need for an innovation that will provide effective sealing between the doctor blade assembly and the housing of the printer cartridge.